Near field communication (nfc) coexistance

ABSTRACT

Certain aspects of the present disclosure are generally directed to apparatus and techniques for protecting electronic devices that may be prone to damage by wireless charging fields. For example, the apparatus may include a wireless charging circuit configured to selectively generate a wireless charging field and an impedance detection circuit coupled to the wireless charging circuit and configured to detect an impedance change corresponding to the wireless charging field. In this case, a proximity detection circuit may selectively detect proximity of one or more electronic devices that are prone to damage by the wireless charging circuit. In some aspects, detecting the proximity of the one or more electronic devices is activated based on detecting the impedance change, and wherein generating the wireless charging field comprises reducing a transmit power of the wireless charging field based on detecting the impedance change.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present application claims the benefit of U.S. ProvisionalApplication Ser. No. 62/337,145, entitled “NEAR FIELD COMMUNICATION(NFC) COEXISTANCE” and filed May 16, 2016, which is assigned to theassignee of the present application and is expressly incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to electronic devices, and inparticular, to wireless charging of electronic devices.

BACKGROUND

An increasing number and variety of electronic devices are powered viarechargeable batteries. Such devices include mobile phones, portablemusic players, laptop computers, tablet computers, computer peripheraldevices, communication devices (e.g., Bluetooth devices), digitalcameras, hearing aids, and the like. While battery technology hasimproved, battery-powered electronic devices increasingly consumegreater amounts of power. As such, these devices are constantlyrecharging. Rechargeable devices are often charged via wired connectionsthat use cables or other similar connectors that are physicallyconnected to a power supply. Cables and similar connectors may sometimesbe inconvenient or cumbersome and have other drawbacks. Wireless powercharging systems, for example, may allow users to charge and/or powerelectronic devices without physical, electrical connections, thusreducing the number of components for operation of the electronicdevices and simplifying the use of the electronic device.

There is flexibility in having different sizes and shapes in thecomponents (e.g., magnetic coil, charging plate, etc.) that make up awireless power transmitter and/or a wireless power receiver in terms ofindustrial design and support for a wide range of devices.

SUMMARY

Certain aspects of the present disclosure are directed to an apparatusfor wireless charging. The apparatus may generally include a wirelesscharging circuit configured to selectively generate a wireless chargingfield, an impedance detection circuit coupled to the wireless chargingcircuit and configured to detect an impedance change corresponding tothe wireless charging field, and a proximity detection circuitconfigured to selectively detect proximity of one or more electronicdevices that are prone to damage by the wireless charging circuit,wherein detecting the proximity of the one or more electronic devices isactivated based on detecting the impedance change, and whereingenerating the wireless charging field comprises reducing a transmitpower of the wireless charging field based on detecting the impedancechange.

Certain aspects of the present disclosure are directed to an apparatusfor wireless charging. The apparatus generally includes a wirelesscharging circuit, a proximity detection circuit, a first coil having afirst terminal coupled to the first wireless charging circuit and asecond terminal coupled to the proximity detection circuit, a secondcoil having a first terminal coupled to the wireless charging circuitand a second terminal coupled to the proximity detection circuit, atleast one first switch coupled between the first terminals of the firstcoil and the second coil, and at least one second switch coupled betweenthe second terminals of the first coil and the second coil.

Certain aspects of the present disclosure are directed to a method forwireless charging. The method generally includes selectively generatinga wireless charging field, detecting an impedance change correspondingto the wireless charging field, and selectively detecting proximity ofone or more electronic devices that are prone to damage by the wirelesscharging field, wherein detecting the proximity of the one or moreelectronic devices is activated based on detecting the impedance change,and wherein generating the wireless charging field comprises reducing atransmit power of the wireless charging field based on detecting theimpedance change.

Certain aspects of the present disclosure are directed to an apparatusfor wireless charging. The apparatus generally includes means forselectively generating a wireless charging field, means for detecting animpedance change corresponding to the wireless charging field, and meansfor selectively detecting proximity of one or more electronic devicesthat are prone to damage by the wireless charging field, whereindetecting the proximity of the one or more electronic devices isactivated based on detecting the impedance change, and wherein means forgenerating the wireless charging field comprises means for reducing atransmit power of the wireless charging field based on detecting theimpedance change.

Certain aspects of the present disclosure are directed to a method forwireless charging for wireless charging. The method generally includesselectively transmitting, during one or more first time intervals, oneor more beacons for detection of one or more electronic devices to becharged, and selectively detecting proximity of one or more otherelectronic devices that are prone to damage by a wireless charging fieldduring one or more second time intervals that are different than the oneor more first time intervals.

Certain aspects of the present disclosure are directed to a method forwireless charging for wireless charging. The method generally includesselectively generating a wireless charging field, and detecting animpedance change corresponding to the wireless charging field, andselectively detecting proximity of one or more electronic devices thatare prone to damage by the wireless charging field, wherein detectingthe proximity of the one or more electronic devices is activated basedon detecting the impedance change, and wherein generating the wirelesscharging field is disabled based on detecting the impedance change,wherein the one or more electronic devices comprise at least one of anear-field communication (NFC) card or radio-frequency identification(RFID) card, and wherein selectively detecting proximity of one or moreelectronic devices comprises modulating a detection field for detectingthe at least one NFC card or RFID card, wherein detecting the at leastone NFC card or RFID card is based on receiving information viamodulation of the detection field by the at least one NFC card or RFIDcard.

Other aspects, features, and embodiments of the present disclosure willbecome apparent to those of ordinary skill in the art, upon reviewingthe following description of specific, exemplary aspects of the presentdisclosure in conjunction with the accompanying figures. While featuresof the present disclosure may be discussed relative to certain aspectsand figures below, all aspects of the present disclosure can include oneor more of the advantageous features discussed herein. In other words,while one or more aspects may be discussed as having certainadvantageous features, one or more of such features may also be used inaccordance with the various aspects of the present disclosure. Insimilar fashion, while exemplary aspects may be discussed below asdevice, system, or method aspects it should be understood that suchexemplary aspects can be implemented in various devices, systems, andmethods.

The following detailed description and accompanying drawings provide abetter understanding of the nature and advantages of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

With respect to the discussion to follow and in particular to thedrawings, it is stressed that the particulars shown represent examplesfor purposes of illustrative discussion, and are presented in the causeof providing a description of principles and conceptual aspects of thepresent disclosure. In this regard, no attempt is made to showimplementation details beyond what is needed for a fundamentalunderstanding of the present disclosure. The discussion to follow, inconjunction with the drawings, makes apparent to those of skill in theart how embodiments in accordance with the present disclosure may bepracticed. In the accompanying drawings:

FIG. 1 is a functional block diagram of a wireless power transfersystem, in accordance with certain aspects of the present disclosure.

FIG. 2 is a functional block diagram of a wireless power transfersystem, in accordance with certain aspects of the present disclosure.

FIG. 3 is a schematic diagram of a portion of transmit circuitry orreceive circuitry of FIG. 2 including a power transmitting or receivingelement, in accordance with certain aspects of the present disclosure.

FIG. 4 illustrates example charging and detection fields, in accordancewith certain aspects of the present disclosure.

FIG. 5 illustrates example charging and detection fields andcorresponding control signals, in accordance with certain aspects of thepresent disclosure.

FIG. 6 illustrates an example wireless charging circuit and proximitydetection circuit sharing a common coil, in accordance with certainaspects of the present disclosure.

FIG. 7 is a flow diagram of example operations for wireless charging andprotection of electronic devices, in accordance with certain aspects ofthe present disclosure.

FIG. 8 is a flow diagram of example operations for wireless charging, inaccordance with certain aspects of the present disclosure.

FIG. 9 is a flow diagram of example operations for wireless chargingincluding beacon transmissions, in accordance with certain aspects ofthe present disclosure.

DETAILED DESCRIPTION

Drawing elements that are common among the following figures may beidentified using the same reference numerals.

Wireless power transfer may refer to transferring any form of energyassociated with electric fields, magnetic fields, electromagneticfields, or otherwise from a transmitter to a receiver without the use ofphysical electrical conductors (e.g., power may be transferred throughfree space). The power output into a wireless field (e.g., a magneticfield or an electromagnetic field) may be received, captured by, orcoupled by a “power receiving element” to achieve power transfer.

FIG. 1 is a functional block diagram of a wireless power transfer system100, in accordance with certain aspects of the present disclosure. Inputpower 102 may be provided to a transmitter 104 from a power source (notshown in this figure) to generate a wireless (e.g., magnetic orelectromagnetic) field 105 for performing energy transfer. A receiver108 may couple to the wireless field 105 and generate output power 110for storing or consumption by a device (not shown in this figure)coupled to the output power 110. The transmitter 104 and the receiver108 may be separated by a distance 112. The transmitter 104 may includea power transmitting element 114 for transmitting/coupling energy to thereceiver 108. The receiver 108 may include a power receiving element 118for receiving or capturing/coupling energy transmitted from thetransmitter 104.

In one illustrative aspect, the transmitter 104 and the receiver 108 maybe configured according to a mutual resonant relationship. When theresonant frequency of the receiver 108 and the resonant frequency of thetransmitter 104 are substantially the same or very close, transmissionlosses between the transmitter 104 and the receiver 108 are reduced. Assuch, wireless power transfer may be provided over larger distances.Resonant inductive coupling techniques may thus allow for improvedefficiency and power transfer over various distances and with a varietyof inductive power transmitting and receiving element configurations.

In certain aspects, the wireless field 105 may correspond to the “nearfield” of the transmitter 104. The near-field may correspond to a regionin which there are strong reactive fields resulting from the currentsand charges in the power transmitting element 114 that minimally radiatepower away from the power transmitting element 114. The near-field maycorrespond to a region that is within about one wavelength (or afraction thereof) of the power transmitting element 114.

In certain aspects, efficient energy transfer may occur by coupling alarge portion of the energy in the wireless field 105 to the powerreceiving element 118 rather than propagating most of the energy in anelectromagnetic wave to the far field.

In certain implementations, the transmitter 104 may output a timevarying magnetic (or electromagnetic) field with a frequencycorresponding to the resonant frequency of the power transmittingelement 114. When the receiver 108 is within the wireless field 105, thetime varying magnetic (or electromagnetic) field may induce a current inthe power receiving element 118. As described above, if the powerreceiving element 118 is configured as a resonant circuit to resonate atthe frequency of the power transmitting element 114, energy may beefficiently transferred. An alternating current (AC) signal induced inthe power receiving element 118 may be rectified to produce a directcurrent (DC) signal that may be provided to charge or to power a load.

FIG. 2 is a functional block diagram of a wireless power transfer system200, in accordance with certain aspects of the present disclosure. Thesystem 200 may include a transmitter 204 and a receiver 208. Thetransmitter 204 (also referred to herein as power transfer unit, PTU)may include transmit circuitry 206 that may include an oscillator 222, adriver circuit 224, and a front-end circuit 226. The oscillator 222 maybe configured to generate an oscillator signal at a desired frequencythat may adjust in response to a frequency control signal 223. Theoscillator 222 may provide the oscillator signal to the driver circuit224. The driver circuit 224 may be configured to drive the powertransmitting element 214 at, for example, a resonant frequency of thepower transmitting element 214 based on an input voltage signal (V_(D))225. The driver circuit 224 may be a switching amplifier configured toreceive a square wave from the oscillator 222 and output a sine wave. Incertain aspects, the transmitter 204 may include an impedance detectioncircuit 242 that may be configured to detect the receiver 208 to becharged by sensing the change in impedance as seen by the driver circuit224 driving the power transmitting element 214.

The front-end circuit 226 may include a filter circuit configured tofilter out harmonics or other unwanted frequencies. The front-endcircuit 226 may include a matching circuit configured to match theimpedance of the transmitter 204 to the impedance of the powertransmitting element 214. As will be explained in more detail below, thefront-end circuit 226 may include a tuning circuit to create a resonantcircuit with the power transmitting element 214. As a result of drivingthe power transmitting element 214, the power transmitting element 214may generate a wireless field 205 to wirelessly output power at a levelsufficient for charging a battery 236, or otherwise powering a load.

The transmitter 204 may further include a controller 240 operablycoupled to the transmit circuitry 206 and configured to control one ormore aspects of the transmit circuitry 206, or accomplish otheroperations relevant to managing the transfer of power. The controller240 may be a micro-controller or a processor. The controller 240 may beimplemented as an application-specific integrated circuit (ASIC). Thecontroller 240 may be operably connected, directly or indirectly, toeach component of the transmit circuitry 206. The controller 240 may befurther configured to receive information from each of the components ofthe transmit circuitry 206 and perform calculations based on thereceived information. The controller 240 may be configured to generatecontrol signals (e.g., signal 223) for each of the components that mayadjust the operation of that component. As such, the controller 240 maybe configured to adjust or manage the power transfer based on a resultof the operations performed by it. The transmitter 204 may furtherinclude a memory (not shown) configured to store data, for example, suchas instructions for causing the controller 240 to perform particularfunctions, such as those related to management of wireless powertransfer. In certain aspects, the transmitter 204 may also include anear-field communication (NFC) circuit and/or radio frequencyidentification (RFID) circuit that may be configured to control thetransmit circuitry 206 for detection of NFC and/or RFID devices. Forexample, the NFC and/or RFID circuits may transmit (e.g., via transmitcircuitry 206) one or more detection fields and detect proximity of NFCand/or RFID devices by detecting modulations of the detection fields.

The receiver 208 (also referred to herein as power receiving unit, PRU)may include receive circuitry 210 that may include a front-end circuit232 and a rectifier circuit 234. The front-end circuit 232 may includematching circuitry configured to match the impedance of the receivecircuitry 210 to the impedance of the power receiving element 218. Aswill be explained below, the front-end circuit 232 may further include atuning circuit to create a resonant circuit with the power receivingelement 218. The rectifier circuit 234 may generate a DC power outputfrom an AC power input to charge the battery 236, as shown in FIG. 2.The receiver 208 and the transmitter 204 may additionally communicate ona separate communication channel 219 (e.g., Bluetooth, Zigbee, cellular,etc.). The receiver 208 and the transmitter 204 may alternativelycommunicate via in-band signaling using characteristics of the wirelessfield 205.

The receiver 208 may be configured to determine whether an amount ofpower transmitted by the transmitter 204 and received by the receiver208 is appropriate for charging the battery 236. In certain aspects, thetransmitter 204 may be configured to generate a predominantlynon-radiative field with a direct field coupling coefficient (k) forproviding energy transfer. Receiver 208 may directly couple to thewireless field 205 and may generate an output power for storing orconsumption by a battery (or load) 236 coupled to the output or receivecircuitry 210.

The receiver 208 may further include a controller 250 configuredsimilarly to the transmit controller 240 as described above for managingone or more aspects of the wireless power receiver 208. The receiver 208may further include a memory (not shown) configured to store data, forexample, such as instructions for causing the controller 250 to performparticular functions, such as those related to management of wirelesspower transfer.

As discussed above, transmitter 204 and receiver 208 may be separated bya distance and may be configured according to a mutual resonantrelationship to minimize transmission losses between the transmitter 204and the receiver 208.

FIG. 3 is a schematic diagram of a portion of the transmit circuitry 206or the receive circuitry 210 of FIG. 2, in accordance with certainaspects of the present disclosure. As illustrated in FIG. 3, transmit orreceive circuitry 350 may include a power transmitting or receivingelement 352 and a tuning circuit 360. The power transmitting orreceiving element 352 may also be referred to or be configured as anantenna or a “loop” antenna. The term “antenna” generally refers to acomponent that may wirelessly output or receive energy for coupling toanother antenna. The power transmitting or receiving element 352 mayalso be referred to herein or be configured as a “magnetic” antenna, oran induction coil, a resonator, or a portion of a resonator. The powertransmitting or receiving element 352 may also be referred to as a coilor resonator of a type that is configured to wirelessly output orreceive power. As used herein, the power transmitting or receivingelement 352 is an example of a “power transfer component” of a type thatis configured to wirelessly output and/or receive power. The powertransmitting or receiving element 352 may include an air core or aphysical core such as a ferrite core (not shown in this figure).

When the power transmitting or receiving element 352 is configured as aresonant circuit or resonator with tuning circuit 360, the resonantfrequency of the power transmitting or receiving element 352 may bebased on the inductance and capacitance. Inductance may be simply theinductance created by a coil and/or other inductor forming the powertransmitting or receiving element 352. Capacitance (e.g., a capacitor)may be provided by the tuning circuit 360 to create a resonant structureat a desired resonant frequency. As a non limiting example, the tuningcircuit 360 may comprise a capacitor 354 and a capacitor 356, which maybe added to the transmit and/or receive circuitry 350 to create aresonant circuit.

The tuning circuit 360 may include other components to form a resonantcircuit with the power transmitting or receiving element 352. As anothernon limiting example, the tuning circuit 360 may include a capacitor(not shown) placed in parallel between the two terminals of thecircuitry 350. Still other designs are possible. In some aspects, thetuning circuit in the front-end circuit 226 may have the same design(e.g., 360) as the tuning circuit in front-end circuit 232. In otheraspects, the front-end circuit 226 may use a tuning circuit designdifferent than in the front-end circuit 232.

For power transmitting elements, the signal 358, with a frequency thatsubstantially corresponds to the resonant frequency of the powertransmitting or receiving element 352, may be an input to the powertransmitting or receiving element 352. For power receiving elements, thesignal 358, with a frequency that substantially corresponds to theresonant frequency of the power transmitting or receiving element 352,may be an output from the power transmitting or receiving element 352.Although aspects disclosed herein may be generally directed to resonantwireless power transfer, persons of ordinary skill will appreciate thataspects disclosed herein may be used in non-resonant implementations forwireless power transfer.

Near Field Communication (NFC) Coexistance With Wireless Charging

Aspects of the present disclosure are generally directed to a dedicatedtransceiver that can detect electronic devices that can potentially bedamaged by wireless charging fields. For example, aspects of the presentdisclosure provide techniques for detection and protection of NFC and/orradio frequency identification (RFID) devices. It should be noted, thatthough certain aspects are described herein with respect to NFC and/orRFID devices, the same principles can be applied to other suitable typesof devices.

NFC or RFID devices can be damaged by the high amplitude magnetic fieldgenerated by wireless chargers. Some devices may be resistant to damageby wireless chargers due to their tuning to a different frequency. Forexample; a frequency of 13.56 MHz may be used for NFC or RFID devicesand a frequency of 6.78 MHz may be used for wireless charging. However,some low quality devices, such as low quality integrated capacitors,have sufficiently low quality factor (Q) that they may be subject todamage from wireless charging fields. For example, low qualitycapacitors may experiences changes in their capacitance value at thepower levels involved when wirelessly charging. In certain aspects, inorder to avoid damage to these devices, the transmission power of thewireless charging field may be reduced, and in some cases disabled, whenthese devices are present.

Certain aspects of the present disclosure may use a dedicated reader forNFC/RFID detection. In certain aspects, NFC/RFID detection may beactivated once the wireless charging field has been deactivated, and anyactivation of the wireless charging field may be prevented if anymodulation is detected, indicating proximity of one or more NFC/RFIDdevices that may be subject to damage by the wireless charging field. Inorder to detect the NFC/RFID devices when the wireless charging field ison, an impedance detection circuit may be used to detect an impedanceshift corresponding to the wireless charging field, based on which thewireless charging field may be deactivated and proximity detection ofthe NFC/RFID devices may be activated.

FIG. 4 illustrates example charging and detection fields, in accordancewith certain aspects of the present disclosure. In FIG. 4, time is shownas increasing along the horizontal axis. Further, periods of time wherethe charging (e.g., along the top axis) and/or detection fields (e.g.,along the bottom axis) are activated are shown as pulses along the axis,while periods of time where the charging is deactivated are shown asempty along the axis.

In certain aspects, a wireless charging circuit may include a powertransmission unit (PTU) 204 configured to generate wireless chargingfields. For example, the PTU 204 may transmit beacon transmissions 404(e.g., beacons) via the power transmitting element 214. The beacontransmissions are small pulses of charging fields used to detect a powerreceiver unit (PRU) to be charged and potentially provide a small amountof power for powering one or more elements of the PRU. For example, animpedance detection circuit 242 coupled to the PTU 204 may detect thePRU to be charged by sensing the change in impedance as seen by thedriver circuit 224 driving the power transmitting element 214. In someaspects, the PTU 204 may detect a PRU to be charged by applying powerfor a duration (e.g., 100 milliseconds) and waiting for the PRU to sendback an acknowledgement that it is receiving power. In some aspects, theacknowledgement may be in the form a connection request for establishinga communication link with the PTU 204. In some cases, the PTU 204 maydetect a PRU to be charged by detecting the device via a proximitysensor such as a weight sensor or an infrared sensor. In other aspects,detection of the PRU may be in part based on detecting an impedancechange presented to the PTU 204 that is above a threshold due toplacement of the PRU within a charging region of the field generated bythe PTU 204.

As illustrated, the PTU 204 may transmit the beacon transmissions 404periodically. The PTU 204 may further include a NFC circuit 244 (or RFIDcircuit to detect RFID devices). The NFC circuit 244 may generatedetection field 405, based on which proximity of NFC devices (e.g., NFCcards) may be detected. For example, the NFC circuit may modulate thedetection field according to an NFC protocol in order to elicitmodulation of the detection field by NFC devices positioned within thedetection field. In response, the NFC devices may modulate the detectionfield in accordance with the NFC protocol, indicating the presence ofthe NFC device to the NFC circuit 244.

As presented above, the NFC devices may be prone to damage by thewireless charging fields. Thus, in certain aspects, once the NFC circuit408 detects an NFC device (e.g., at 406), the PTU 204 may deactivate thetransmission of the wireless charging fields (e.g., beacon transmissions404). The NFC circuit 408 may continue to transmit the detection field405 to sense when the NFC device is no longer in proximity (e.g., at410), based on which the PTU 204 may reactivate the charging fieldtransmission.

Certain aspects of the present disclosure are directed to detectingproximity of an electronic device while a PRU is being wirelesslycharged. For example, at 412, a PRU may be placed in proximity to thePTU 204 and detected by the PTU 204 based on the beacon transmissions404. For example, an impedance detection circuit 242 coupled to the PTU204 may detect the PRU by sensing the change in impedance as seen by thedriver circuit 224 driving the power transmitting element 214. In thiscase, the wireless charging of the PRU by the PTU 204 begins. In certainaspects, the impedance detection circuit 242 coupled to the PTU 204 maybe configured to detect an impedance change (e.g., at 414) of the powertransmitting element 214 generating the wireless charging field duringthe charging process. For example, the impedance detection circuit 242may detect an impedance change by detecting a change in impedance of asignal (e.g., a power supply signal) presented to the wireless chargingcircuit while generating the wireless charging field. The impedancechange may indicate that an electronic device may be in proximity to thePTU 204.

In certain aspects, to reduce the likelihood of false proximitydetection, which may be caused by, for example, PRU load modulations,the detected impedance change may be compared to other impedance changeinformation such as a profile of impedance changes detected by theimpedance detection circuit 242. Thus, based on the detected impedancechange, PTU 204 may deactivate the wireless charging field and the NFCcircuit 408 may activate the detection field transmission (e.g.,detection field 422) to determine whether an NFC device is in proximityto the PTU. If the NFC circuit 408 does not detect proximity of an NFCdevice, the PTU 204 may resume wireless charging (e.g., at 416).Otherwise, if an NFC device is detected, the wireless charging mayremain deactivated. For example, at 418, an NFC device may be placed inproximity to the PTU 204, causing the impedance detection circuit 242coupled to the PTU 204 to detect an impedance change at 418. Thus, thePTU 204 may deactivate the wireless charging field transmission, and theNFC circuit 408 may activate the NFC detection field transmission. Inthis case, the NFC circuit 408 may detect proximity of an NFC device,and the wireless charging may remain deactivated until the NFC device isremoved at 420 (e.g., as detected by the NFC circuit 408).

FIG. 5 illustrates example charging and detection fields, in accordancewith certain aspects of the present disclosure. In certain aspects, thedetection fields generated by the NFC circuit 408 may continue for a setdetection interval. For example, the NFC circuit 408 may generate adetection field that may continue for a detection interval 502. In thiscase, the PTU 204 may continue to send beacon transmissions 404 todetect a PRU to be charged, even during the detection interval 502.However, once the PTU 204 detects a PRU to be charged and begins thetransmission of wireless charging fields, no further detection intervalsare initiated. For example, the NFC circuit 408 may include a processor504 (e.g., microprocessor μP). The processor 504 may receive anNFC_DETECT_ENABLE signal from the PTU 204, indicating whether the NFCcircuit 408 should activate NFC detection. For example, when theNFC_DETECT_ENABLE signal is logic high, it may indicate that NFCdetection may continue, when the PTU 204 is not transmitting a wirelesscharging field. That is, if the NFC_DETECT_ENABLE signal is logic high,a detection interval can be initiated, and if the NFC_DETECT_ENABLEsignal is logic low, a detection interval cannot be initiated. Incertain aspects, the wireless charging field may be prevented fromactivating (e.g., deactivated) whenever the NFC_DETECT_ENABLE signal islogic high.

During the detection intervals (e.g., detection interval 502), the NFCcircuit 408 may detect an NFC device, and communicate the detection ofthe NFC device to the PTU 204 via the NFC_CARD_FOUND signal. Forexample, at 506, the NFC circuit 408 may detect an NFC device, and theprocessor 504 may switch the NFC_CARD_FOUND signal from logic low, tologic high, indicating proximity of an NFC device. When theNFC_CARD_FOUND signal is switched to logic high, the NFC_DETECT_ENABLEsignal may also be kept at logic high. Thus, the PTU 204 may deactivatethe transmission of the wireless charging fields (e.g., beacons). At508, the NFC device may be removed, the NFC_CARD_FOUND signal may switchto logic low along with the NFC_DETECT_ENABLE signal, and the wirelesscharging field transmissions may resume.

As described above with respect to FIG. 4, the proximity of anelectronic device may be detected during a charging phase based on adetection of an impedance change corresponding to the wireless chargingfield. For example, the PTU 204 may detect an impedance change of thepower transmitting element 214 generating the wireless charging field at510. Based on the detection of the impedance change, the PTU 204 mayswitch NFC_DETECT_ENABLE signal to logic high, allowing for a detectioninterval to begin, as illustrated. If an NFC device is not detected, thePTU 204 may switch the NFC_DETECT_ENABLE signal back to logic low andwireless charging may resume. If an NFC device is detected, theprocessor 504 may switch the NFC_CARD_FOUND signal to logic high,deactivating any transmission of a wireless charging field until the NFCdevice is removed. For example, at 511, the PTU 204 may detect animpedance change corresponding to the charging field and a detectioninterval may begin. In this case, an NFC device is detected by the NFCcircuit 408. Thus, the processor 504 of the NFC circuit 408 switches theNFC_CARD_FOUND signal to logic high, the PTU 204 switches theNFC_DETECT_ENABLE signal to logic high, and any transmission of awireless charging field is deactivated until the NFC device is removedat 512.

In certain aspects, the PTU 204 and the NFC circuit 244 may use coils ofa similar shape so that the NFC detection field matches the wirelesscharging field. If the coils are more than slightly different, there maybe nulls and peaks that do not align, increasing the possibility ofdamage to electronic devices.

In certain aspects, separate coils may be used for the PTU 204 and theNFC circuit 244. However, in some cases, a shared coil may be used forthe PTU 204 and the NFC circuit 244. In either case, the parasitic loadswhen the wireless charging field is active should be reduced to maintainefficiency, and the NFC device should be tuned to operate over the samerange of conditions as the amplifier of the wireless charging circuit,including detuning due to devices on the coils. Reduction of theparasitic load may be achieved via series switches with low seriescapacitance.

In certain aspects, the NFC coil may be configured to have low Q, whichmay be accomplished using series resistors. Using series resistors maybe advantageous in certain aspects since low field effect transistor(FET) off capacitance is often a traded off for high FET on resistance,allowing the FET resistance to reduce coil Q. Series resistors allow thecoil to float, preventing them from back-conducting through the FETdiodes. Dual coils have the benefit of slightly reduced coupling betweenthe two amplifiers. The two coils may be similar and close such thattheir coupling can be high, but not as high as a direct connection.

In certain aspects, sharing a single coil removes the additional cost ofa duplicate coil, and the protection circuitry is approximatelyequivalent in both cases, reducing bill-of-materials (BOM) costs ascompared to the dual coil option. However, such a shared coil may resultin dual feeds that may detune each other, and there may be thepossibility of damage, particularly to the NFC amplifier from the highvoltages present from the wireless charging amplifier. In certainaspects, the shared coil option may differ from the dual coil system inthat the detuning may be implemented via a shunt detuning circuit. Onesolution may be to use a protection circuit to isolate the NFC amplifierfrom the system, and taking the existing components on the wirelesscharging path into account when tuning the NFC path.

FIG. 6 illustrates an example wireless charging circuit and proximitydetection circuit sharing a common coil, in accordance with certainaspects of the present disclosure. In certain aspects, a power amplifier(PA) 602 for the PTU may be coupled to a PTU tuning circuit 604, whichmay be coupled to a first terminal 606 of a coil 608 and a firstterminal 610 of a coil 612. An NFC PA 614 for the NFC circuit may becoupled to an NFC tuning circuit 616, which may be coupled to a secondterminal 618 of the coil 608 and a second terminal 620 of the coil 612.

In certain aspects, isolation circuitry may be used to electricallyisolate the wireless charging circuitry (e.g., PTU PA 602 and PTU tuningcircuit 604) from the coils 608 and 612 during operation of the NFC, andvice versa. For example, a first set of cascode connected transistors622 may be coupled between the terminals 606 and 610, and a second setof cascode connected transistors 624 may be coupled between terminals618 and 620. During wireless charging, the transistors 624 mayelectrically couple the terminals 618 and 620, effectively shorting andrendering the terminals 618 and 620 as a center tap for the coils 608and 612. In some cases, the transistors 624 may electrically couple theterminals 618 and 620 to a reference potential (e.g., an electricalground potential). During operation of the NFC (e.g., proximitydetection), transistors 622 may electrically couple the terminals 606and 610, effectively shorting and rendering the terminals 606 and 610 asa center tap for the coils 608 and 612. In some cases, the transistors622 may electrically couple the terminals 606 and 610 to a referencepotential (e.g., an electrical ground potential). For example, the gateterminals of transistors 622 may be driven by an NFC_SELECT signal, andgate terminals of the transistors 624 may be driven by an inverse of theNFC_SELECT signal, which may be generated by an inverter 626. Therefore,by selectively coupling the terminals 606 and 610, or terminals 618 and620, during proximity detection and wireless charging, respectively, thecharging field and detection field can be tuned separately (e.g.independently). That is, during wireless charging, the PTU tuningcircuit 604 can tune the wireless charging field without impact from theNFC circuitry, and during proximity detection, the NFC tuning circuit616 can tune the detection field without impact from the wirelesscharging circuitry.

In certain aspects, the proximity detection may involve emulatingvarious aspects of NFC/RFID standards. For example, in some cases, thetransmission of the detection field may be modulated to induce cards(electronic devices such as NFC or RFID cards) to respond. In somecases, any modulation by the card may be detected to indicate proximityas opposed to detecting only valid responses.

In certain aspects, a custom NFC reader may be implemented using anexisting PA. This approach may be implemented with improved (faster andmore sensitive) modulation detection on the PRU as well as retuning ofthe PA matching circuits. This approach would allow reuse of the samecircuitry for both wireless charging and proximity detection (e.g., NFCcircuit), so the wireless charging could also benefit from the improvedsensing. In certain aspects, additional parallel tuning capacitors maybe switched in or out to change the tuning from 6.78 MHz (for wirelesscharging) to 13.56 MHz (for proximity detection via NFC), or potentiallyidentifying a tuning circuit that operates acceptably for both. Incertain aspects, the sensing circuit may be an in-phase/quadrature-phase(I/Q) demodulator, which could be dual-purposed for wireless chargingfield impedance detection and NFC modulation detection.

In certain aspects, the wireless charging field and a proximitydetection field (e.g., for the NFC) may be transmitted simultaneously,either with separate PAs, antennas, or by inducing 2nd order harmonicson the wireless charging field. By transmitting the wireless chargingfield and a proximity detection field simultaneously, always-onbackground scanning can be implemented.

FIG. 7 is a flow diagram of example operations 700 for wirelesscharging, in accordance with certain aspects of the present disclosure.The operations 700 may be performed by a circuit, such as the circuitsof FIGS. 1-6.

The operations 700 may begin, at block 702, by interleaving beacontransmissions (e.g., beacon transmissions 404) and NFC detection fieldtransmissions, as described with respect to FIGS. 4 and 5. At block 704,the circuit may determine whether an NFC/RFID device or PRU is detected.If not, the circuit may continue the beacon and NFC detection fieldtransmissions at block 702. If an NFC/RFID device is detected, thetransmit power of the beacon transmission 404 may be reduced (ordisabled) and continuous detection field transmissions may begin atblock 706. At block 708, the circuit determines whether the NFC/RFIDdevice is removed (e.g., via the detection field transmission). If so,the circuit begins the interleaved beacon and detection fieldtransmissions at block 702. Otherwise, detection field transmission atblock 706 continues.

At block 704, if a PRU is detected, the circuit reduces the transmitpower of (or disables) the beacon and detection field transmissions andbegins, at block 710, transmitting the wireless charging field to begincharging the detected PRU. At block 712, the circuit may either detectan impedance shift or detect that the PRU is removed. Otherwise, thecharging field transmissions continue at block 710. If an impedanceshift is detected, the circuit reduces the transmit power of (ordisables) the charging field transmissions and begins transmitting thedetection field, at block 714, to detect whether an NFC/RFID device isin proximity. At block 716, the circuit detects the NFC/RFID device. Ifthe NFC-RFID device is detected, the transmission of the detection fieldcontinues. Otherwise, the circuit again begins the transmission of thecharging field at block 710. At block 712, if the circuit detects thatthe PRU is removed, the circuit begins the interleaved transmission ofthe beacon and detection fields at block 702.

FIG. 8 is a flow diagram of example operations 800 for wirelesscharging, in accordance with certain aspects of the present disclosure.The operations 800 may be performed by a circuit, such as the circuitsof FIGS. 1-6.

The operations 800 may begin, at block 802, by selectively generating awireless charging field. At block 804, an impedance change correspondingto the wireless charging field may be detected. At block 806, theoperations 800 continue by selectively detecting proximity of one ormore electronic devices that are prone to damage by the wirelesscharging circuit, wherein detecting the proximity of the one or moreelectronic devices is activated based on detecting the impedance change,and wherein generating the wireless charging field comprises reducing atransmit power of the wireless charging field based on detecting theimpedance change. In certain aspects, reducing the transmit power of thewireless charging field comprises disabling the generation of thewireless charging field.

In certain aspects, the one or more electronic devices comprise at leastone of an near field communication (NFC) card or radio-frequencyidentification (RFID) card. In some cases, selectively detectingproximity of one or more electronic devices comprises modulating adetection field for detecting the at least one NFC card or RFID card,and detecting the at least one NFC card or RFID card is based onreceiving information via modulation of the detection field by the atleast one NFC card or RFID card.

In certain aspects, selectively generating the wireless charging fieldmay include selectively transmitting, during one or more first timeintervals, one or more beacons for detection of one or more otherelectronic devices to be charged. In this case, selectively detectingproximity of the electronic devices selectively may include detectingproximity of the electronic devices during one or more second timeintervals that are different than the one or more first time intervals.In certain aspects, transmitting the one or more beacons is disabledbased on the proximity of the one or more electronic devices.

In certain aspects, generating the wireless charging field and theproximity detection is performed via a shared coil. In this case,circuitry used for generating the wireless charging field may beelectrically isolated from the shared coil when detecting proximity ofthe electronic devices is activated. In some cases, circuitry used fordetecting proximity of the electronic devices may be electricallyisolated from the shared coil when generating the wireless chargingfield is activated.

In certain aspects, detecting proximity of the electronic devices isperformed while generating the wireless charging field. In certainaspects, detecting proximity of the one or more electronic devicescomprises transmitting a detection field and detecting modulations inthe detection field. In some cases, transmitting the detection fieldcomprises modulating the detection field.

FIG. 9 is a flow diagram of example operations 900 for wirelesscharging, in accordance with certain aspects of the present disclosure.The operations 900 may be performed by a circuit, such as the circuitsof FIGS. 1-6.

The operations 900 may begin, at block 902, by selectively transmitting,during one or more first time intervals, one or more beacons fordetection of one or more electronic devices to be charged. At block 904,the circuit may selectively detect proximity of the electronic devicescomprises selectively detecting proximity of the electronic devicesduring one or more second time intervals that are different than the oneor more first time intervals.

In certain aspects, transmitting the one or more beacons is disabledbased on the detected proximity of the one or more other electronicdevices. In some cases, the one or more other electronic devicescomprise at least one of an NFC card or a radio-frequency identification(RFID) card, wherein the transmitting the one or more beacons isdisabled based on the detected proximity of the least one of the NFCcard or the RFID card. In certain aspects, the wireless charging circuitis configured to charge the one or more electronic devices by generatinga wireless charging field based on the detection of the one or moreother electronic devices via the one or more beacons. In certainaspects, the operations 900 also include detecting an impedance changecorresponding to the wireless charging field, wherein the generating thewireless charging field is disabled based on the detected impedancechange.

While certain examples provided herein have described proximitydetection with respect to an NFC device to facilitate understanding,aspects of the present disclosure may be applied to any other type ofcircuit configured to detect proximity of electronic devices. Forexample, proximity detection may be performed via RFID circuitry.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication-specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database, or another data structure), ascertaining, and thelike. Also, “determining” may include receiving (e.g., receivinginformation), accessing (e.g., accessing data in a memory), and thelike. Also, “determining” may include resolving, selecting, choosing,establishing, and the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an ASIC, a field programmable gate array (FPGA) or otherprogrammable logic device (PLD), discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor maybe a microprocessor, but in the alternative, the processor may be anycommercially available processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in hardware, anexample hardware configuration may comprise a processing system in awireless node. The processing system may be implemented with a busarchitecture. The bus may include any number of interconnecting busesand bridges depending on the specific application of the processingsystem and the overall design constraints. The bus may link togethervarious circuits including a processor, machine-readable media, and abus interface. The bus interface may be used to connect a networkadapter, among other things, to the processing system via the bus. Thenetwork adapter may be used to implement the signal processing functionsof the physical (PHY) layer. In the case of a user terminal, a userinterface (e.g., keypad, display, mouse, joystick, etc.) may also beconnected to the bus. The bus may also link various other circuits suchas timing sources, peripherals, voltage regulators, power managementcircuits, and the like, which are well known in the art, and therefore,will not be described any further.

The processing system may be configured as a general-purpose processingsystem with one or more microprocessors providing the processorfunctionality and external memory providing at least a portion of themachine-readable media, all linked together with other supportingcircuitry through an external bus architecture. Alternatively, theprocessing system may be implemented with an ASIC with the processor,the bus interface, the user interface in the case of an accessterminal), supporting circuitry, and at least a portion of themachine-readable media integrated into a single chip, or with one ormore FPGAs, PLDs, controllers, state machines, gated logic, discretehardware components, or any other suitable circuitry, or any combinationof circuits that can perform the various functionality describedthroughout this disclosure. Those skilled in the art will recognize howbest to implement the described functionality for the processing systemdepending on the particular application and the overall designconstraints imposed on the overall system.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. An apparatus for wireless charging, comprising: awireless charging circuit configured to selectively generate a wirelesscharging field; and an impedance detection circuit coupled to thewireless charging circuit and configured to detect an impedance changecorresponding to the wireless charging field; and a proximity detectioncircuit configured to selectively detect proximity of one or moreelectronic devices that are prone to damage by the wireless chargingcircuit, wherein detecting the proximity of the one or more electronicdevices is activated based on detecting the impedance change, andwherein generating the wireless charging field comprises reducing atransmit power of the wireless charging field based on detecting theimpedance change.
 2. The apparatus of claim 1, wherein reducing thetransmit power of the wireless charging field comprises disabling thegeneration of the wireless charging field.
 3. The apparatus of claim 1,wherein the one or more electronic devices comprise at least one of annear field communication (NFC) card or radio-frequency identification(RFID) card and the proximity detection circuit comprises circuitryconfigured to modulate a detection field for detecting the at least oneNFC card or RFID card, wherein detecting the at least one NFC card orRFID card is based on receiving information via modulation of thedetection field by the at least one NFC card or RFID card.
 4. Theapparatus of claim 1, wherein: the wireless charging circuit isconfigured to selectively transmit, during one or more first timeintervals, one or more beacons for detection of one or more otherelectronic devices to be charged; and the proximity detection circuit isconfigured to selectively detect proximity of the one or more electronicdevices during one or more second time intervals that are different thanthe one or more first time intervals.
 5. The apparatus of claim 4,wherein transmitting the one or more beacons is disabled based on theproximity of the one or more electronic devices.
 6. The apparatus ofclaim 4, wherein the one or more electronic devices comprise at leastone of an NFC card or a radio-frequency identification (RFID) card,wherein the transmitting the one or more beacons is disabled based onthe detected proximity of the least one of the NFC card or the RFIDcard.
 7. The apparatus of claim 4, wherein the wireless charging circuitis configured to charge the one or more other electronic devices bygenerating the wireless charging field based on the detection of the oneor more other electronic devices via the one or more beacons.
 8. Theapparatus of claim 1, wherein detecting the impedance change comprisesdetecting a change in impedance of a signal presented to the wirelesscharging circuit while generating the wireless charging field.
 9. Theapparatus of claim 1, wherein the wireless charging circuit and theproximity detection circuit share at least one coil.
 10. The apparatusof claim 9, wherein: the at least one coil comprises a first coil and asecond coil; a first terminal of the first coil and a first terminal ofthe second coil are coupled to the wireless charging circuit; and asecond terminal of the first coil and a second terminal of the secondcoil are coupled to the proximity detection circuit.
 11. The apparatusof claim 10, wherein the first terminal of the first coil and the firstterminal of the second coil are coupled when generating the wirelesscharging field is activated.
 12. The apparatus of claim 10, wherein thesecond terminal of the first coil and the second terminal of the secondcoil are coupled when detecting proximity of the one or more electronicdevices is activated.
 13. The apparatus of claim 10, wherein: thewireless charging circuit comprises a first amplifier having an outputcoupled to a first tuning circuit that is coupled to the first terminalsof the first and second coils; and the proximity detection circuitcomprises a second amplifier having an output coupled to a second tuningcircuit that is coupled to the second terminals of the first and secondcoils; and the apparatus further comprises an isolation circuitconfigured to electrically couple the first terminals of the first andsecond coils during wireless charging and the second terminals of thefirst and second coils during proximity detection.
 14. The apparatus ofclaim 13, wherein the isolation circuit is configured to electricallycouple the first and second terminals of the first and second coils to areference potential.
 15. The apparatus claim 1, wherein the proximitydetection circuit comprises an in-phase and quadrature (I/Q) demodulatorconfigured to detect proximity of the electronic devices, and whereinthe I/Q demodulator is also used for detecting the impedance changecorresponding to the wireless charging field.
 16. The apparatus of claim1, wherein detecting proximity of the one or more electronic devicescomprises transmitting a detection field and detecting modulations inthe detection field, wherein transmitting the detection field comprisesmodulating the detection field.
 17. An apparatus for wireless charging,comprising: a wireless charging circuit; a proximity detection circuit;a first coil having a first terminal coupled to the first wirelesscharging circuit and a second terminal coupled to the proximitydetection circuit; a second coil having a first terminal coupled to thewireless charging circuit and a second terminal coupled to the proximitydetection circuit; at least one first switch coupled between the firstterminals of the first coil and the second coil; and at least one secondswitch coupled between the second terminals of the first coil and thesecond coil.
 18. The apparatus of claim 17, wherein: the wirelesscharging circuit further comprises: a first tuning circuit coupled tothe first terminals of the first coil and the second coil; and a firstamplifier coupled to the first tuning circuit; and the proximitydetection circuit comprises: a second tuning circuit coupled to thesecond terminals of the first coil and the second coil; and a secondamplifier coupled to the second tuning circuit.
 19. The apparatus ofclaim 17, wherein: the second switch is closed during operation of thewireless charging circuit; and the first switch is closed duringoperation of the proximity detection circuit.
 20. A method for wirelesscharging, comprising: selectively generating a wireless charging field;detecting an impedance change corresponding to the wireless chargingfield; and selectively detecting proximity of one or more electronicdevices that are prone to damage by the wireless charging field, whereindetecting the proximity of the one or more electronic devices isactivated based on detecting the impedance change, and whereingenerating the wireless charging field comprises reducing a transmitpower of the wireless charging field based on detecting the impedancechange.
 21. The method of claim 20, wherein the one or more electronicdevices comprise at least one of an near field communication (NFC) cardor radio-frequency identification (RFID) card, and wherein selectivelydetecting proximity of one or more electronic devices comprisesmodulating a detection field for detecting the at least one NFC card orRFID card, wherein detecting the at least one NFC card or RFID card isbased on receiving information via modulation of the detection field bythe at least one NFC card or RFID card.
 22. The method of claim 20,wherein: selectively generating the wireless charging field comprisesselectively transmitting, during one or more first time intervals, oneor more beacons for detection of one or more other electronic devices tobe charged; and selectively detecting proximity of the electronicdevices comprises selectively detecting proximity of the electronicdevices during one or more second time intervals that are different thanthe one or more first time intervals.
 23. The method of claim 22,wherein transmitting the one or more beacons is disabled based on theproximity of the one or more electronic devices.
 24. The method of claim20, wherein generating the wireless charging field and the proximitydetection is performed via a shared coil, the method further comprising:electrically isolating circuitry used for generating the wirelesscharging field from the shared coil when detecting proximity of theelectronic devices is activated.
 25. The method of claim 20, whereingenerating the wireless charging field and the proximity detection isperformed via a shared coil, the method further comprising: electricallyisolating circuitry used for detecting proximity of the electronicdevices from the shared coil when generating the wireless charging fieldis activated.
 26. The method of claim 20, wherein detecting proximity ofthe electronic devices is performed while generating the wirelesscharging field.
 27. The method of claim 20, wherein detecting proximityof the one or more electronic devices comprises transmitting a detectionfield and detecting modulations in the detection field.
 28. A method forwireless charging, comprising: selectively generating a wirelesscharging field; and detecting an impedance change corresponding to thewireless charging field; and selectively detecting proximity of one ormore electronic devices that are prone to damage by the wirelesscharging field, wherein detecting the proximity of the one or moreelectronic devices is activated based on detecting the impedance change,and wherein generating the wireless charging field is disabled based ondetecting the impedance change, wherein the one or more electronicdevices comprise at least one of an near field communication (NFC) cardor radio-frequency identification (RFID) card, and wherein selectivelydetecting proximity of one or more electronic devices comprisesmodulating a detection field for detecting the at least one NFC card orRFID card, wherein detecting the at least one NFC card or RFID card isbased on receiving information via modulation of the detection field bythe at least one NFC card or RFID card.
 29. The method of claim 28,wherein: selectively generating the wireless charging field comprisesselectively transmitting, during one or more first time intervals, oneor more beacons for detection of one or more other electronic devices tobe charged; and selectively detecting proximity of the electronicdevices comprises selectively detecting proximity of the electronicdevices during one or more second time intervals that are different thanthe one or more first time intervals.
 30. The method of claim 29,wherein transmitting the one or more beacons is disabled based on thedetected proximity of the one or more other electronic devices.